This present invention relates to a high efficiency, high work coefficient fan which can be used, for example, in electronics cooling applications.
Many prior art cooling fans include a motor-driven impeller which propels a stream of air through a fan housing. These fans may also comprise an outlet guide vane assembly which is positioned downstream of the impeller to both de-swirl and increase the static pressure of the air, and a diffuser section which is located downstream of the outlet guide vane assembly to decelerate and thereby further increase the static pressure of the air.
The impeller and the outlet guide vane assembly each include a plurality of radially extending blades or vanes. The shape of each blade or vane can be defined by the values of camber, chord and stagger for each of a plurality of radially spaced airfoil segments in the blade or vane, as well as the degrees of lean and bow for each of the leading and trailing edges of the blade or vane. In addition, the overall configuration of the impeller and the outlet guide vane assembly can be defined in terms of the solidity and aspect ratio of the blades or vanes as a whole.
In the inventors' experience, prior art cooling fans typically have total-to-static efficiencies of less than 60%. Low fan efficiencies require the use of larger and heavier motors which must operate at higher speeds. These motors usually require increased power to operate, generate more noise and have reduced life spans. Fan inefficiencies may result from virtually any choice made during the design process, from architecture selection through the detailed design of the flowpath surfaces, the impeller blades and the guide vanes.
Prior art cooling fans use bow and lean in the impeller blades and guide vanes in order to achieve certain desired performance characteristics. In prior art cooling fans in which the flow near the midspan of the blades or vanes is weak, however, increasing the bow and lean angles may be detrimental since it would increase the aerodynamic loading near the midspan. Because the flow near the midspan is already weak, additional loading from increased bow would lead to increased flow separation and poorer performance. This is especially true for smaller fans with lower aspect ratio impeller blades and guide vanes.